1. Field of the Invention
This invention relates to wind turbines and more particularly to a vertical axis high speed wind turbine in which the aerodynamic control of the rotational speed is achieved over its entire operational mode, i.e., the starting, normal operation and braking.
2. Prior Art
Generally, various wind turbines converting wind energy to a rotary motion have been already suggested and practiced. Among them, the propeller wind turbine (horizontal axis wind turbine) is required to have the propeller rotating disk always rightly aligned with the wind direction, whereas the vertical axis wind turbine is omni-directional, is not influenced at all by the wind direction and is better in respect of the configuration and operation.
Therefore, the present inventors have developed and suggested a vertical axis high speed wind turbine using blades of an efficient airfoil.
In the above mentioned vertical axis high speed wind turbine, the efficiency is high but the starting torque is low. Further, in the general wind turbines, at the time of such excessive wind velocity as in a typhoon, it will be necessary to control the rotational speed. Therefore, in order to practice this kind of vertical axis turbine, it is necessary to develop a means of controlling its rotational speed.